Tom Sawyer on sun 6 feb 05
I have a question for makers of large planters. I have been making some
large planters for my personal use; With great effort I turn these over and
add a pedistal and I usually dry them upside down and often keep them
covered for varying periods of time and yes I compresss the bottoms while
throwing many times and with great care. I place drainage holes in the
bottom often three almost always two when they are leather hard and at the
time when the pedistal is added. I am also making some large vases and bowls
and never have a cracking problem even though they have wide bottoms. I'm
thinking that the drainage holes are somehow related; perhaps there is
accelerated drying around the holes which in turn promote cracking. My
question is what do other makers of large planters do about drainage holes;
Could they promote cracking and if they are used when should they be created
and what precautions should one take. Thanks.
Tom Sawyer
tsawyer@cfl.rr.com
Victoria E. Hamilton on mon 7 feb 05
Tom,
If you are concerned that your drainage holes may be the cause of cracking,
try applying wax resist to the holes, and to some of the area around the
holes to retard drying.
You might also look at the even-ness of your planters - if the bottom turns
out to be significantly thinner (before or after turning) than the walls of
the planter, this could certainly contribute to the problem.
Victoria Hamilton
Millennia Antica Pottery
Seattle, WA
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Tom Sawyer
Sent: Sunday, February 06, 2005 20:19
To: CLAYART@LSV.CERAMICS.ORG
Subject: Large Planters & Cracking Bottoms
I have a question for makers of large planters. I have been making some
large planters for my personal use; With great effort I turn these over and
add a pedistal and I usually dry them upside down and often keep them
covered for varying periods of time and yes I compresss the bottoms while
throwing many times and with great care. I place drainage holes in the
bottom often three almost always two when they are leather hard and at the
time when the pedistal is added. I am also making some large vases and bowls
and never have a cracking problem even though they have wide bottoms. I'm
thinking that the drainage holes are somehow related; perhaps there is
accelerated drying around the holes which in turn promote cracking. My
question is what do other makers of large planters do about drainage holes;
Could they promote cracking and if they are used when should they be created
and what precautions should one take. Thanks.
Tom Sawyer
tsawyer@cfl.rr.com
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claybair on tue 8 feb 05
I haven't made such large planters as Tom and Mike but when I had cracking
around my planter holes I found taking the sharp edge off with a damp sponge
or finger eliminated the cracking. It might have been softening up that
sharp edge or just compressing the area.
Gayle Bair
Bainbridge Island, WA
http://claybair.com
-----Original Message-----
From: Mike Gordon
Tom,
I throw 25lb up to 50lb. planters and I have had few problems with
cracking. Where do the cracks appear? I only put one hole in the center
of the bottom about the size of a quarter. Sometimes I see small
hairline cracks radiating out from the hole, so the thickness of the
bottom around the hole could be a problem. I fire at C/6, Mike Gordon
On Feb 6, 2005, at 8:18 PM, Tom Sawyer wrote:
> I have a question for makers of large planters. I have been making some
> large planters for my personal use; With great effort I turn these
> over and
> add a pedistal and I usually dry them upside down and often keep them
> covered for varying periods of time and yes I compresss the bottoms
> while
> throwing many times and with great care. I place drainage holes in the
> bottom often three almost always two when they are leather hard and at
> the
> time when the pedistal is added. I am also making some large vases and
> bowls
> and never have a cracking problem even though they have wide bottoms.
> I'm
> thinking that the drainage holes are somehow related; perhaps there is
> accelerated drying around the holes which in turn promote cracking. My
> question is what do other makers of large planters do about drainage
> holes;
> Could they promote cracking and if they are used when should they be
> created
> and what precautions should one take. Thanks.
>
>
>
> Tom Sawyer
>
> tsawyer@cfl.rr.com
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Alex Solla on tue 8 feb 05
Tom-
We make a few dozen LARGE planters at a time... not a great big part of our business, but like Tony said, it helps show off the other little stuff we make.
The most straight forward answer for you: work wet. If you can flip your forms as soon as the rims are stiff enough not to collapse, the bottoms will usually still be wet enough to nearly throw.... soft mud... might still be close to sagging there. That is usually when I add my drainage holes. Also gives me an opportunity to decide if I even want to keep the bottom. Sometimes we just cut it off, add a coil and throw a new bottom, or make it conical.... you get the picture. Always more fun working with wet mud than dry.
If for some reason you have to wait till your forms are leatherhard, another suggestion would be to cut your drainage holes with a hole cutter, ie a circular tube, usually brass with a cutout... rather than a drill...creates more of a slicing motion through the clay as opposed to distorting the clay and leading to cracking.
Good luck.
-Alex Solla
Cold Springs Studio
Trumansburg, NY
Tom Sawyer wrote:
I have a question for makers of large planters. I have been making some
large planters for my personal use; With great effort I turn these over and
add a pedistal and I usually dry them upside down and often keep them
covered for varying periods of time and yes I compresss the bottoms while
throwing many times and with great care. I place drainage holes in the
bottom often three almost always two when they are leather hard and at the
time when the pedistal is added. I am also making some large vases and bowls
and never have a cracking problem even though they have wide bottoms. I'm
thinking that the drainage holes are somehow related; perhaps there is
accelerated drying around the holes which in turn promote cracking. My
question is what do other makers of large planters do about drainage holes;
Could they promote cracking and if they are used when should they be created
and what precautions should one take. Thanks.
Tom Sawyer
tsawyer@cfl.rr.com
______________________________________________________________________________
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You may look at the archives for the list or change your subscription
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Mike Gordon on tue 8 feb 05
Tom,
I throw 25lb up to 50lb. planters and I have had few problems with
cracking. Where do the cracks appear? I only put one hole in the center
of the bottom about the size of a quarter. Sometimes I see small
hairline cracks radiating out from the hole, so the thickness of the
bottom around the hole could be a problem. I fire at C/6, Mike Gordon
On Feb 6, 2005, at 8:18 PM, Tom Sawyer wrote:
> I have a question for makers of large planters. I have been making some
> large planters for my personal use; With great effort I turn these
> over and
> add a pedistal and I usually dry them upside down and often keep them
> covered for varying periods of time and yes I compresss the bottoms
> while
> throwing many times and with great care. I place drainage holes in the
> bottom often three almost always two when they are leather hard and at
> the
> time when the pedistal is added. I am also making some large vases and
> bowls
> and never have a cracking problem even though they have wide bottoms.
> I'm
> thinking that the drainage holes are somehow related; perhaps there is
> accelerated drying around the holes which in turn promote cracking. My
> question is what do other makers of large planters do about drainage
> holes;
> Could they promote cracking and if they are used when should they be
> created
> and what precautions should one take. Thanks.
>
>
>
> Tom Sawyer
>
> tsawyer@cfl.rr.com
>
> _______________________________________________________________________
> _______
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
Cindy in SD on tue 8 feb 05
Dear Tom,
I've had better luck with putting holes in the bottom of pots if I
smooth and thin down the edges of the holes. This seems particularly
important on larger pieces--I think the thicker walls have something to
do with this.
Now it's your turn to come up with some advice. The problem I have with
large planters on pedestals is that I have a hard time keeping the
pedestals from cracking off (or at least partly cracking off) either
during drying or firing. I do dry them very slowly and try to add the
pedestals as soon as I can possibly turn the pot over. I score and slip
and use coils and magic water. Any hints?
Thanks,
Cindy in SD
Dave Finkelnburg on tue 8 feb 05
Tom,
As you know well, in general the last place to dry is the first place to crack. That's because the dryer parts of the pot pull together and put tension on the wet spots. This is, of course, only an issue if you get different rates of drying between the foot and rim.
You may be cracking the ware by putting the hole in at leather hard. The softer the clay is when you make the three holes, the better the chance that won't be an issue. For what it's worth, I throw a hole in the center and that usually does all that's necessary for drainage.
Regards,
Dave Finkelnburg
Tom Sawyer wrote:
My
question is what do other makers of large planters do about drainage holes;
Could they promote cracking and if they are used when should they be created
and what precautions should one take. Thanks.
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Ama Menec on tue 8 feb 05
I was always taught to throw plant pots, of any size, with the drainage hole
made during the initial opening out, i.e. once the clay is centred, drive
your hands down until the fingertips touch the wheel head, open up the
drainage hole, and then lift your hands up a bit to pull out the rest of the
base. This I was taught by two brilliant technicians at University, who had
both worked at a large hand made plant pot company making very large
planters; and this practice formed the early part of my big-ware throwing
tuition. I don't recall any cracking of the bases, and they never mentioned
the possibility.
Ama, Totnes, Devon.
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Ivor and Olive Lewis on tue 8 feb 05
Dear Tom Sawyer,
It is my belief that relatively large holes, or several smaller holes
distributed equally about the area of the base, will act as points of
stress relief.
It is possible to prevent small cracks from propagating by drilling a
hole at the terminating points of new cracks.
Rather than three holes I would use four, with one in the centre and
the others equally spaced in a equilateral triangle about the central
hole
A pity clay is not transparent otherwise you would be able to make
the stress patterns observable with the aid of polarised light.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Tom Sawyer on tue 8 feb 05
Cindy,
Oddly, I virtually never have the pedestals crack - just the bottoms near
where I place the drainage holes. I do much like you describe, I score the
pot bottom and pedestal bottom, use magic water and coil the joins inside
and out. My cracking of the bottom seems somehow to relate to the drainage
holes; I've got three large pots almost dry that are doing nicely and
showing no signs of cracking but I haven't placed any drainage holes as of
yet.
Tom Sawyer
tsawyer@cfl.rr.com
Tom Sawyer on tue 8 feb 05
Mike,
In reply the cracking is often hairline and as you describe it usually
radiates from around the hole{s}. I've got three pots in progress now which
do not have holes [I thinking of adding them when dry} and so far there is
no cracking. I'm convinced the cracking is related to the drainage hole{s}.
Thanks
Tom Sawyer
tsawyer@cfl.rr.com
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Mike Gordon
Sent: Tuesday, February 08, 2005 11:13 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Large Planters & Cracking Bottoms
Tom,
I throw 25lb up to 50lb. planters and I have had few problems with
cracking. Where do the cracks appear? I only put one hole in the center
of the bottom about the size of a quarter. Sometimes I see small
hairline cracks radiating out from the hole, so the thickness of the
bottom around the hole could be a problem. I fire at C/6, Mike Gordon
On Feb 6, 2005, at 8:18 PM, Tom Sawyer wrote:
> I have a question for makers of large planters. I have been making some
> large planters for my personal use; With great effort I turn these
> over and
> add a pedistal and I usually dry them upside down and often keep them
> covered for varying periods of time and yes I compresss the bottoms
> while
> throwing many times and with great care. I place drainage holes in the
> bottom often three almost always two when they are leather hard and at
> the
> time when the pedistal is added. I am also making some large vases and
> bowls
> and never have a cracking problem even though they have wide bottoms.
> I'm
> thinking that the drainage holes are somehow related; perhaps there is
> accelerated drying around the holes which in turn promote cracking. My
> question is what do other makers of large planters do about drainage
> holes;
> Could they promote cracking and if they are used when should they be
> created
> and what precautions should one take. Thanks.
>
>
>
> Tom Sawyer
>
> tsawyer@cfl.rr.com
>
> _______________________________________________________________________
> _______
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
____________________________________________________________________________
__
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
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Lee Love on wed 9 feb 05
Tom,
What kind of clay are you using? My Mashiko nami is resistant
to cracking. My Shigaraki clay cracks if you look at it funny. The
nami is coarse & sandy.
--
in Mashiko, Japan http://mashiko.org
http://potters.blogspot.com/ WEB LOG
http://claycraft.blogspot.com/ Photos!
ELizabeth Gowen on wed 9 feb 05
Tom I am having a similar problem around the drainage holes. I have used =
2
different clay bodies, earthenware and porcelain, have used a tube to =
twist
or push as well as a hand held drill bit. Done it on wet, dry and =
leather
hard clay and so far the only one that has not cracked is the one done =
with
a drill bit on bone dry porcelain, hasn't been fired yet. My hopes are =
for
the latter. Perhaps with the wet and leather clay the clay is being =
pushed
as well as cut creating stress that the bone doesn't get? I did support =
the
bone dry with a block of wood under where I cut since these have a =
turned
foot. I did not support the leather or the wet clay ones. Also perhaps =
there
is some compression with the wetter ones around the whole because one =
pushes
a bit while cutting where with the bone dry one is careful just to cut
lightly with the drill bit? Thinking out loud.
Liz Gowen NJ USA
bonnie staffel on wed 9 feb 05
When I make planters of any size, I make two small mouse holes on the lowest
side of the pot. No cracking. I make this as I build the pot using a
thick rounded stick. It leaves a lump of clay that is pushed inside, but I
clean that off when leather hard. Most times I throw an attached saucer
when making planters. Then to make them waterproof on the bottom, fire them
upside down on posts with a non glazed interior, and glaze on the outside
bottom.
Warm regards,
Bonnie Staffel
http://webpages.charter.net/bstaffel/
http://vasefinder.com/bstaffelgallery1.html
Charter Member Potters Council
Michael Wendt on wed 9 feb 05
Tom,
I think you are on the right track with the timing issue with respect to the
holes cracking.
My clay does the same thing when holes are cut at the wrong time. Rather
than waste large planters for the test, you could try a simple set of
experiments that use a clay disk of the same thickness.
In the sample disk, cut one hole using an oiled piece of very thin copper
tubing before you wire off the bat, label that. Cut a second hole using the
same method after wiring. Cut holes by various methods at different stages
of drying and label those. Drill a hole when the greenware is completely
dry. Finally, drill the last hole in the bisqued
disk and then hard fire the disk exactly the way you have been firing the
planters. If you label each and keep notes, one experimental disk may be
enough.
If none of these methods solves the hole cracking problem, it may well be
the clay body is at fault. In that case, repeat the experiment with the new
clay body.
My theory on hole cracks is that grog or sand is at fault. The cutting
process sets up small tears caused by the cutting implement dragging the
grog or sand down through the cut face along the hole surface and as drying
proceeds, these tears propagate. Use of an oiled pipe often smoothes the
hole edge enough to overcome the tearing problem.
In sinks, I cut the hole wet , then final trim and burnish the hole as soon
as the sink can be inverted. Burnishing cut and drilled surfaces will often
overcome cracking around holes by reintegrating the torn material into a
sound surface without any crack start points.
I finally resorted to drilling holes in lamp bases after they were bisque
fired to beat the occasional cracking problem arising from the drilled
holes.
Best of luck, and it was fun to meet you in Mendocino,
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
Tom wrote:
My question is what do other makers of large planters do about drainage
holes;
Could they promote cracking and if they are used when should they be created
and what precautions should one take. Thanks.
Tom Sawyer
Mike Gordon on wed 9 feb 05
Tom,
I also just drill the bisque sometimes, which works as well, Mike Gordon
On Feb 8, 2005, at 6:46 PM, Tom Sawyer wrote:
> Mike,
> In reply the cracking is often hairline and as you describe it usually
> radiates from around the hole{s}. I've got three pots in progress now
> which
> do not have holes [I thinking of adding them when dry} and so far
> there is
> no cracking. I'm convinced the cracking is related to the drainage
> hole{s}.
> Thanks
> Tom Sawyer
> tsawyer@cfl.rr.com
>
> -----Original Message-----
> From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Mike
> Gordon
> Sent: Tuesday, February 08, 2005 11:13 AM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: Large Planters & Cracking Bottoms
>
> Tom,
> I throw 25lb up to 50lb. planters and I have had few problems with
> cracking. Where do the cracks appear? I only put one hole in the center
> of the bottom about the size of a quarter. Sometimes I see small
> hairline cracks radiating out from the hole, so the thickness of the
> bottom around the hole could be a problem. I fire at C/6, Mike Gordon
> On Feb 6, 2005, at 8:18 PM, Tom Sawyer wrote:
>
>> I have a question for makers of large planters. I have been making
>> some
>> large planters for my personal use; With great effort I turn these
>> over and
>> add a pedistal and I usually dry them upside down and often keep them
>> covered for varying periods of time and yes I compresss the bottoms
>> while
>> throwing many times and with great care. I place drainage holes in the
>> bottom often three almost always two when they are leather hard and at
>> the
>> time when the pedistal is added. I am also making some large vases and
>> bowls
>> and never have a cracking problem even though they have wide bottoms.
>> I'm
>> thinking that the drainage holes are somehow related; perhaps there is
>> accelerated drying around the holes which in turn promote cracking. My
>> question is what do other makers of large planters do about drainage
>> holes;
>> Could they promote cracking and if they are used when should they be
>> created
>> and what precautions should one take. Thanks.
>>
>>
>>
>> Tom Sawyer
>>
>> tsawyer@cfl.rr.com
>>
>> ______________________________________________________________________
>> _
>> _______
>> Send postings to clayart@lsv.ceramics.org
>>
>> You may look at the archives for the list or change your subscription
>> settings from http://www.ceramics.org/clayart/
>>
>> Moderator of the list is Mel Jacobson who may be reached at
>> melpots@pclink.com.
>>
>
> _______________________________________________________________________
> _____
> __
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
> _______________________________________________________________________
> _______
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
Tom Sawyer on wed 9 feb 05
There have been several good suggestion; two that I particularly liked were
to use wax resist around the holes and another was to make a center hole
when throwing the bottom. I plan to try both methods. I'm glad I asked
because it is obvious others are having this problem. I certain its not my
clay because I have other pieces such as vases and bowls with equally large
bottoms that never crack.
Tom Sawyer
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of ELizabeth Gowen
Sent: Wednesday, February 09, 2005 7:23 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Large Planters & Cracking Bottoms
Tom I am having a similar problem around the drainage holes. I have used 2
different clay bodies, earthenware and porcelain, have used a tube to twist
or push as well as a hand held drill bit. Done it on wet, dry and leather
hard clay and so far the only one that has not cracked is the one done with
a drill bit on bone dry porcelain, hasn't been fired yet. My hopes are for
the latter. Perhaps with the wet and leather clay the clay is being pushed
as well as cut creating stress that the bone doesn't get? I did support the
bone dry with a block of wood under where I cut since these have a turned
foot. I did not support the leather or the wet clay ones. Also perhaps there
is some compression with the wetter ones around the whole because one pushes
a bit while cutting where with the bone dry one is careful just to cut
lightly with the drill bit? Thinking out loud.
Liz Gowen NJ USA
____________________________________________________________________________
__
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
Ivor and Olive Lewis on thu 10 feb 05
Dear Ama,
A fine illustration of industrial behavioural psychology.
The process is part of the design and the whole is engineered for
efficiency.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Steve Mills on fri 11 feb 05
I used to make pedestal planters. I learnt from a local Gardenware
Potter and added a bit of discovery of my own.
The Pedestal is made and fired separately and has a spigot on the top
which corresponds with a largish thrown hole in the base of the bowl.
The bowl I bisque fired on three squares of Ceramic Fibre (which were
constantly re-used) otherwise its own weight pins it to the non slippery
surface of the shelf and it cracked because it couldn't shrink easily.
The bowl was glaze fired to cone 9 on a bed of sand or Molochite
depending on which clay I had used.
Once I had sorted out the above routine I never lost any again.
Drawing available to interested parties.
Steve
Bath
UK
>> I have a question for makers of large planters. I have been making some
>> large planters for my personal use; With great effort I turn these
>> over and
>> add a pedistal and I usually dry them upside down and often keep them
>> covered for varying periods of time and yes I compresss the bottoms
>> while
--
Steve Mills
Bath
UK
Michael Wendt on sat 12 feb 05
Cindy,
Yours is a common problem we all share. The best way to solve it is with a
trial run of different methods all on the same test piece and all labeled.
Try first a joint with only a few drops of water between it and the pot. Do
not score or slip. Instead, wiggle the foot enough to cause it to bond and
exude a little slip around the joint. Take a plastic handled pin tool,
sharpen it to a point in a pencil sharpener and use the fine tip to radius
the connection between the foot and the pot bottom. Label it and write a
notation in your note book.
Choose a second , third and even fourth joining method and do the same for
each.
When done, see if any of them have worked.
Choose the one that is the quickest that works and still gives you the look
you want.
Each clay body prefers a different joint method so it may be necessary to
repeat this test for each type of clay you use.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
Cindy wrote:
Now it's your turn to come up with some advice. The problem I have with
large planters on pedestals is that I have a hard time keeping the
pedestals from cracking off (or at least partly cracking off) either
during drying or firing. I do dry them very slowly and try to add the
pedestals as soon as I can possibly turn the pot over. I score and slip
and use coils and magic water. Any hints?
Thanks,
Cindy in SD
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